1. Field of Invention
The present invention refers to an electric heating cooker and its control method, especially a kind of electrical heating cooker with weighing function and weighing control method thereof. It belongs to the field of electric heating appliance used in kitchen.
2. Description of Related Arts
Traditionally the electric heating cooker has the function of boiling and steaming, such as automatic rice cooker, electric pressure cooker, electric ceramic cooker or electromagnetic furnace. When cooking, they measure the change of temperature or the pressure in the cooker, or they set the length of cooking time to control the whole process of cooking. But in fact during the cooking with the change of temperature in the cooker, the water vapor will go out which results in the change of the weight of the whole cooker. And the speed of evaporating vapor reflects the boiling status of the water in the cooker and the amount of the remaining water therein.
Additionally when cooking the user don't have an exact idea of how much water to be put into the cooker according to the amount of food. If more water is added the rice will be softer and it takes more time to cook, which is a waste of electric energy. If less water is added the rice will be harder and it will easily stick to the cooker, which is a waste food. Sometimes according to cook recipe users are required to add several grams of cooking oil, several grams of salts or tens of grams of auxiliary ingredient. But it's hard for users to add the weight to the precision of several grams.
FIG. 1 is a weight change curve S1 of the whole automatic rice cooker during cooking rice which is a typical representative of the traditional electrical heating cooker.
The X-axis is the time axis. The Y-axis is the weight axis of the whole cooker. At t00 there is nothing added in the cooker. The weight of the whole cooker is (mc).
(A) is called as add-main-ingredient stage. From t00 uncooked dry rice having a weight of (mp) is added into the cooker. Then the weight of the whole cooker is (mc+mp).
(B) is called as add-water stage. From t10 water having a weight of (mw) is added into the cooker. Then the weight of the whole cooker is (mc+mp+mw).
(C) is called as calm stage. From t20, the cooker is heated with an initial electrical power U0. At this stage because almost no vapor goes out from the cooker, the weight change is so tiny as to ignore. The absolute value of the slope Kc, which shows the speed of weight change of the whole cooker, approaches 0.
(D) is called as pre-boiling stage. At this stage heating power is still U0. The temperature of the lower part of the water becomes higher and higher. It begins to boil partially. Vapor begins to go out from the cooker. But the upper part of the water doesn't boil yet. So at this stage although Kc is increasing, it doesn't reach to the maximum value Kmax.
(E) is called as boiling stage. At this stage the heating power is still U0. All of the water in the cooker is boiling. Vapor tries to go out as fast as possible. But because of the constraint of the vapor outlet of cooker vapor goes out at a relatively constant speed. So at this stage Kc reaches to the maximum value Kmax and keeps near this constant value Kmax.
(F) is called as boiling-ending stage. At this stage the heating power is still U0. All of the water in the cooker is boiling. But because most of the water in the cooker has evaporated from the cooker, the remaining water becomes less and less, and the vapor which goes out becomes less and less. So at this stage Kc decreases slowly from Kmax.
(G) is called as heat preservation stage. At t60 because of the lack of water in the cooker the temperature of the bottom of the cooker increases sharply, which causes the electric heating cooker to trip out, thus enters the heat preservation stage. Then the electric heating cooker starts to preserve heat with another heating power Uk. The whole process of cooking rice is completed. At this point the weight of rice cooked is mf, and the weight of the whole cooker is (mc+mf). It can be seen that mf>mp because the uncooked rice absorbs water and gets heavier. The weight of the evaporated water is (mp+mw−mf).
Research indicates that using the same cooker, adding the same weight of mp of dry rice, adding the same weight of (mw) of water and heating with the same heat power U0, the whole process complies with the weight change curve S1. At the end the same weight of (mf) is got. The error is several grams.
FIG. 2 is a weight change curve S2 of the whole automatic rice cooker which is a typical representative of the traditional electrical heating cooker during cooking porridge or stewing meat or cooking soup.
Compared with S1, S2 is some similar. The difference is that during S2 in addition to adding main ingredient such as rice, pork, chicken, etc, other auxiliary ingredients are required to be added in as well. For example a small amount of mung beans maybe required to be added in for cooking porridge. Red date, Semen Nelumbinis and star anise maybe required to be added in for stewing chicken. So after (A) add-main-ingredient stage, another staged is added, named (A1) add-auxiliary-ingredient stage. Assume the number of the kinds of auxiliary ingredients is N, the weight of each auxiliary ingredient required is (mai), total weight of auxiliary ingredients is (ma=ma1+ma2+ . . . +mai+maN). After that is the (B) add-water stage as well. At this time the total weight of the cooker is (mc+mp+ma+mw). The next are (C) calm stage, (D) pre-boiling stage and (E) boiling stage. But during stewing or cooking porridge or cooking soup users normally will not evaporate all the water in the cooker and will leave much water in cooker to form soup juice. So after the (E) boiling stage, Kc will always keep near the constant value Kmax. It depends on the user's experience to decide when to end this cooking. Because there is no lack of water in at the bottom of the cooker, no tripping out due to sharply increased temperature is exsisted. Therefore, there is no (F) boiling-ending stage. The last to enter is (G) heat preservation stage. The electric heating cooker starts heat preservation with another heating power UK. This completes the process of cooking porridge or stewing meat or cooking soup. At this point the weight of the whole cooker is (mc+mf).
Research indicates that using the same cooker, adding the same weight of mp of main ingredient, adding the same weight of (ma) of auxiliary ingredients, adding the same weight of (mw) of water and heating with the same heat power U0, the whole process complies with the weight change curve S2. At the end the same weight of (mf) is got. The error is several grams.
When using other electric heating cookers such as electric ceramic cooker or electromagnetic furnace to cook food, the similar weight change curve S1 or S2 is got.
According to Chinese cooking custom called ‘Big fire to boil food and then small fire to stew food’, it requires to adequately extend the time length of (E) boiling stage of S1 curve or S2. If (F) boiling-ending stage exists, extend the time length of (F) boiling-ending stage too. In order to extend the time length of (E) or (F), different heating power at different time points is required to be used, in such a manner that water evaporates more slowly and food exists in the boiling water longer. But traditional electric heating cookers use one heating power U0 to cook until the heat preservation stage. They have no good way to use different power at different points. They either measure the temperature of the water in the cooker or set the heating time to control the process. Without an exact idea, users depend on their experience to decide how much water to be added for the given amount of food ingredient. A conventional way to control electric heating cooker is often a fuzzy control method. Even for the same weight of food, due to the weight of water added by users is different in each time, the flavor, e.g., the rice cooked is some soft or some hard or that the soup cooked is some light or some strong, is different each time.
In addition, traditional electric heating cookers can't make user to choose the flavor each time according to the user's different favorite. For example this user wants the rice cooked to be softer, medium or harder. Or this user wants the flavor of the soup cooked to be lighter, medium or stronger. Traditional electric heating cookers can't let users to do such choice. And Traditional electric heating cookers lack intelligence. They can't adjust themselves according to the user's feedback after eating the food cooked thereby. For example, if this time the user expects the hardness of the rice cooked to be medium, but actually the rice cooked is some what harder than the user's expectancy. Traditional electric heating cookers have no way to adjust themselves according to the user's feedback so as to be closer to the user's taste for the cooking next time.
Additionally, now people pay more attention to the healthy of diet. Factors that affect the health of people include that everyday people eat too much salt or cook oil, or eat the food that has too much heat quantity, cholesterol, protein or fat, or eat two kinds of food together which will be bad to health if mixed. A research from China indicates that in China averagely a man eats 12 g of salt everyday, and averagely 15˜18 g of salt in the North of China and 10 g of salt in the South. Eating too much salt causes the disease of hypertension, which has been a ‘silent killer’ of the Chinese heath. Thus, people should eat less salt to prevent and control hypertension. Eating too much cholesterol each day is bad for blood vessel of brain; too much heat quantity, protein or fat will causes the diseases of fat, hyperlipaemia, cardiovascular and cerebrovascular; Sometimes if two kinds of food cooked together will affect the heath, which are called unmatched foods. For example, people will get calculus disease easily if they eat spinach and Tofu cooked together. World Health Organization advocates that everyday each man eats 5˜6 g of salt and has a healthy and bland diet. The cook oil which has more unsaturated fatty acid and less saturated fatty acid is advised. Usually 25 g of oil is enough for the daily diet of a man. Thus, it is necessary for people to know clearly how much salt, cook oil, heat quantity, cholesterol, protein and fat they have taken for the daily diet. There are paper tables which list cholesterol content, heat quantity content, etc for 100 g of various foods or list unmatched food to cook together. But it's hard for people to look up and calculate. It requires people themselves to calculate according to the actual weight of food. And people often have not weighed the accurate weight of food. For example people will often add salt or oil according to their experience which is not accurate. It's difficult for users to control the precision of several grams.
In view of the above defects of traditional electric heating cookers, the researcher of this invention has introduced an electric heating cooker with weighting function and a weighing control method thereof, and it can display the content of heat quantity, cholesterol, protein, fat, salt and cook oil for the food cooked thereby